Adiabatic planar waveguide coupler transformer

ABSTRACT

A solar cell includes a waveguide core for receiving light, a first layer formed on the waveguide core, a second layer formed on the first layer, a third layer formed on the second layer, first metalization coupled to the first layer, and second metalization coupled to the third layer. The first layer comprises a first optical film which varies in an index of refraction in a lateral direction between a first input end where the light is received and a first output end where the light is emitted. In some embodiments, wherein one or more of the first, second, or third layers has a tapered lateral thickness. In some embodiments, the first, second, and third layers form a PIN device. In some embodiments, the waveguide core has a first index of refraction that is lower than respective indexes of refraction for the first, second, and third layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/791,001 filed on Oct. 23, 2017, now U.S. Pat. No. 9,989,701which is a continuation of U.S. patent application Ser. No. 15/149,492filed on May 9, 2016, now U.S. Pat. No. 9,798,082, which is a divisionalof U.S. patent application Ser. No. 14/078,168 filed on Nov. 12, 2013,now U.S. Pat. No. 9,366,816, which claims benefit of priority to U.S.Provisional Application Ser. No. 61/725,400 filed on Nov. 12, 2012, allof which are each herein incorporated by reference in their entirety.

BACKGROUND 1. Field of Invention

Embodiments of the present invention are directed towards efficientcoupling of light and, in particular, to adiabatic planar waveguidecouplers and their applications.

2. Discussion of Related Art

Efficient Coupling of light emitted or received by high index and highnumerical aperture (NA) devices, such as organic light emitting diodes(OLEDs), light emitting diodes (LEDs) and Laser diodes, has not beenavailable other than through discrete devices such as lenses andgratings. Such coupling is also hindered due to the lack of transparent,high index optical materials having an index n above the range ofapproximately 1.44 to 1.7 for such discrete devices. Transparent oxidesand dielectrics are often prepared by melting or sintering of lowmelting precursors, for example with flame hydrolysis precursors. Highlydoped glass is also used to form transparent optical films. Glass filmscomposed of suitably transparent materials are limited to doped glasssuch as borophosphosilicate glass (BPSG), which can be deposited as afilm and then heated to optically clarity. In general, high meltingoxides have higher index of refraction and require refractorytemperatures. However, such materials recrystallize upon cooling and aretherefore not applicable to low loss optical applications due toincreased scattering. In addition, reflection of light at an interfacebetween a device with a first index of refraction and a second devicewith a different index of refraction is a further significant limitationto efficient coupling, transport, transmission and conversion of light.Coupling between adjacent optical elements with widely differingcharacteristics of étendue or optical size and solid angle, requireddiscrete optical elements such as lenses, gratings or so called“photonic crystals” in order to transform the divergence or the opticalsize, or both, for coupling to a second device with different opticalcharacteristics. To date, there has not been an optical coupler whichwas able to couple and transform in one continuous device. Consequently,it has not been possible to integrate high index film layers to form awaveguide structure having a larger index contrast.

Scientific modeling confirms that the measured efficiency of discretelens-based coupling devices such as a single mode laser diode to anoptical fiber is less than about 20-30% after optimization.Consequently, fiber coupled sources are less than about 15% efficient.Similarly, out coupling of an LED to air is less than about 30-40%efficient in production due to the high numeric aperture (NA) of diodedevices, which are typically lateral wave guide devices where light isout coupled generally through the p-side window and through atransparent conductor layer. Similarly, collection from a concentratingmirror is limited to less than about 40%, even for high f-number (longdistance focal point) mirrors, and is typically much less with lowf-number mirrors that are more compact and cost effective concentrators.Out coupling of OLEDs, which have recently been shown to be 100%efficient internally, can result in less than 20 to 25% of the lightbeing actually extracted.

Therefore, there is a need for better production of materials directedto coupling light into and out of discrete devices, waveguides and fibermore efficiently.

SUMMARY

Some embodiments according to the present invention include a method ofdepositing materials to provide for efficient coupling of light from afirst device to a second device, the method including mounting one ormore wafers on a rotating table; continuously rotating the rotatingtable under one or more source targets; providing a process gas;powering the one or more source targets; biasing the one or more waferswith an RF bias; and depositing an optical dielectric film on the one ormore wafers. In some embodiments, a shadow mask can be laterallytranslated across the one or more wafers during deposition. In someembodiments, deposited films can have lateral and/or horizontalvariation in index of refraction and/or lateral variation in thickness.

These and other embodiments are further described below with respect tothe following Figures.

DESCRIPTION OF FIGURES

FIG. 1A illustrates the optical emission solid angle of a typical LED.

FIG. 1B shows deposition of a material on a substrate to form a lateraltaper.

FIG. 1C shows a cross section of the tapered core of the waveguide modesize converter formed under the shadow mask.

FIG. 1D shows a tapered region with a gradual taper.

FIGS. 2A and 2B shows a schematic of an active tapered film forming amode size converter.

FIGS. 2C through 2F illustrate a mode size converter.

FIG. 3 illustrates a planar waveguide coupler design with an LED chip.

FIGS. 4A through 4F show a mask and fixture for providing a shadow maskto a wafer.

FIGS. 5A, 5B, and 5C illustrate a deposition system that can be used todeposit materials according to some embodiments of the presentinvention.

FIG. 5D shows a Tango Systems AXcela PVD sputter system that operates asillustrated in FIGS. 5A-5C.

FIG. 5E shows a process chamber for the system illustrated in FIG. 5D.

FIG. 5F shows two sequential substrate positions on the rotating table,underneath the sputter target position, in the process chamberillustrated in FIG. 5D.

FIG. 5G shows the triangular ‘Delta’ sputter source with metallictarget, removed and facing up, that can be used in the systemillustrated in FIG. 5D.

FIG. 5H shows the rotating table in a process chamber as illustrated inFIG. 5D.

FIG. 5I illustrates an example process for deposition of materialaccording to some embodiments of the present invention.

FIGS. 6A and 6B illustrate lateral coating portions through a lateralmoving shadow mask on a substrate.

FIG. 6C shows the cross section of a waveguide device with layersaccumulated through lateral movement of a shadow mask with deposition ofa film with varying index according to some embodiments of the presentinvention.

FIG. 7 shows a cross section of a device having layers formed accordingto some embodiments of the present invention.

FIG. 8 shows the installation design of the shadow mask position ‘clock’drives in the AXcela rotary inline process chamber according to someembodiments of the present invention.

FIGS. 9A and 9B show some aspects of the clock drive and shadow maskdriven by rotation of the cogged wheel by a chamber pin.

FIG. 10 is an illustration showing the drive pin engaged with the coggedwheel.

FIG. 11 shows a lift mechanism according to some embodiments of thepresent invention.

FIGS. 12 A through 12D show the ellipsometer data for the optical indexand extinction values for films made according to aspects of the presentinvention.

FIG. 12E shows a scanning electron microscope image of a cross sectionof a titanium dioxide coating on a substrate with an amorphous phase orlayer portion and a crystalline layer portion.

FIG. 12F shows n and k data for two films of titanium dioxide depositedaccording some embodiments of the present invention.

FIG. 12G shows ellipsometry data n and k for two amorphous alloy filmsdeposited according to some embodiments of the present invention.

FIG. 12H shows the increase in index for a HfO₂ film sputter depositedwith bias compared to the same film deposited without RF bias.

FIG. 12I shows the range of index for four films: TiO₂, an alloy of TiO₂and HfO₂; HfO2; and Al₂O₃, each deposited according to embodiments ofthe present invention.

FIG. 12J shows the extinction value for three films according toembodiments of the present invention.

FIG. 12K shows the index of refraction of TiO₂ films alloyed with HfO₂over a range of sputter power according to some embodiments of thepresent invention.

FIG. 12L shows the index of a range of TiO₂ films alloyed with HfO2 overa range of sputter power according to some embodiments of the presentinvention.

FIG. 13 shows a process for deposition of materials that uses a clockdrive to move a mask over a wafer during the deposition processaccording to some embodiments of the present invention.

FIG. 14 illustrates the cross section of a coating on a substrateaccording to some embodiments of the present invention.

FIG. 15 shows a core wave guide series of portions representing stagesof a continuous process of forming a first layer such that the thicknessof the coating is continuously increased according to some embodimentsof the present invention.

FIG. 16 shows the cross section of a first layer of constant thicknesswith gradually varying index of refraction under a second layer so as toform a light guiding structure according to some embodiments of thepresent invention.

FIG. 17 illustrates layers of a device for in-coupling or out-couplinglight, both specular and diffuse, according to some embodiments of thepresent invention.

FIG. 18 shows that about 50% of the light emitted from an OLED structureis trapped by a wave guide of high index OLED and transparent conductiveoxide ITO.

FIG. 19 shows a perspective view of layers of a device according to someembodiments of the present invention.

FIG. 20A shows a rendering of an edge emitting diode with three layerscomprising the light emitting waveguide structure of a light emittingdiode or pin structure according to some embodiments of the presentinvention.

FIG. 20B illustrates the tapered core of FIG. 20A within a waveguidestructure according to some embodiments of the present invention.

FIG. 20C is an elevation perspective of the diode and waveguidestructure of FIG. 20B illustrating the path of the light from the diodeaccording to some embodiments of the present invention.

FIG. 21 shows the coupled waveguide structure of FIG. 20C showing thepackaging of the diode with two heat sink structures, one on eitherprimary planar side of the diode, according to some embodiments of thepresent invention.

FIG. 22 shows the overlap of a three layer diode structure with awaveguide structure according to some embodiments of the presentinvention.

FIG. 23 shows a luminaire coupler planar package with a diode sourceaccording to some embodiments as illustrated above in comparison with aconventional light source.

FIG. 24 shows three edge emitting diodes, right aligned with a waveguidecoupler transformer according to some embodiments of the presentinvention.

FIG. 25 shows a waveguide coupler aligned with three diodes and packagedon the surface of a substrate according to some embodiments of thepresent invention.

FIG. 26 shows the assembly of FIG. 25 joined to a heat dissipationdevice according to some embodiments of the present invention.

FIG. 27 shows two devices as shown in FIG. 25 fastened to a heatdissipation device according to some embodiments of the presentinvention.

FIG. 28 shows three diode facets located with a coupler transformeraccording to some embodiments of the present invention.

FIG. 29 shows a coupler transformer according to some embodiments of thepresent invention.

FIG. 30A and FIG. 30B show the plan and perspective view, respectively,of a substrate with three offset layers according to some embodiments ofthe present invention.

FIGS. 31A through 31B show the three offset layers of FIGS. 30A and 30Bin perspective.

FIGS. 32A and 32B show electrical connection of three layer lateralabsorbing solar cells formed in the code of a waveguide and connected inseries so as to provide additive voltage at a reduced current accordingto some embodiments of the present invention.

FIG. 33 shows a lateral absorbing photovoltaic cell in the waveguidehaving a series transformer for out coupling below band light into anoptical fiber for transport according to some embodiments of the presentinvention.

FIG. 34 shows a system for the concentration, coupling and transport oflight to an optical receiver according to some embodiments of thepresent invention.

FIG. 35 illustrates optical attenuation in heavy fluoride glasses ZBLAN(ZrF4-BaF2-LaF3-AlF3-NaF compounds) as compared with Silica.

FIG. 36 illustrates a graph of and fit index as a function of the powerratio of TiO₂ and HfO₂ deposited according to embodiments of the presentinvention.

These and other embodiments of the invention are further discussed belowwith reference to the above figures.

DETAILED DESCRIPTION

It is to be understood that the detailed description provided below areexemplary and explanatory only and are not restrictive of the invention,which is limited only by the attached claims. Further, specificexplanations or theories regarding the deposition of materials or theperformance of wave guide structures according to some embodiments ofthe present invention are presented for explanation only and are not tobe considered limiting with respect to the scope of the presentdisclosure or the claims.

Aspects of embodiments of the present invention include materials,deposition processes to produce the materials, and devices produced fromthe materials for efficient coupling, transport and transformation ofoptical energy throughput, étendue and related luminous energy. Asdescribed below, some structures according to the present invention canhave a variable composite index structure through the thickness oracross the thickness or both that may facilitate light coupling andtransport via bound mode propagation and transformation.

In the following disclosure, the following terms and acronyms are giventheir ordinary meaning and are discussed below only for clarity:

étendue: The étendue of an optical system characterizes the ability ofan optical system to accept light and is a product of the area of theemitting source and the solid angle into which the light propagates. Theétendue is proportional to the square of the numerical aperture (NA) inthat the étendue of light crossing an area S is proportional to theproduct of the area and NA².Numerical Aperture (NA): The Numerical Aperture of an optical system isgiven by n sin θ where n is the index of refraction of the medium inwhich the optical system is operating and θ is the half-angle of themaximum cone of light that can enter or exit the system.f-number: The f-number is typically given by the ratio of the focallength to the diameter of the entrance of a lens system.index of refraction (n): The index of refraction (n) of a material is amaterial property given by the ration of the speed of light in vacuumand the speed of light in the material.

Some embodiments efficiently provide luminance flux (i.e. opticalenergy) into and out of planar thin film and macroscopic waveguidedevices or between other optical devices. Such optical devices includelight emitting materials (e.g. semiconducting materials), high indexmaterials, and high numerical aperture (i.e. high étendue opticalsystems). Adiabatic coupling of optical devices with other devices ofsimilar étendue, including some semiconductor materials and otherdevices, can be accomplished over a range of refractive indices. Someembodiments provide energy coupling, transformation and transport ofoptical luminance with little or no loss of optical energy or powerbetween devices having high or diverse étendue. Some embodiments providefor optical energy collection, transformation and transport as well inorder that the optical energy can be efficiently converted toelectrical, chemical or thermal energy in a device.

As is well known, the étendue of an optical system characterizes theability of an optical system to accept light and is a product of thearea of the emitting source and the solid angle into which itpropagates. Looking through an optical system the étendue can beconserved or, in the presence of dispersion, absorption or other lossmechanisms, increased. Due to conservation principles, the étendue isdifficult to decrease. As is discussed below, however, devices with anadiabatic variation of refractive index and layer thickness can reducethe étendue.

Embodiments of the present invention are related to materials, materialdepositions and devices for the efficient and adiabatic or low-losscoupling and transport of optical energy in planar and macroscopicwaveguide devices. Such deposited materials include a wide range ofrefractive index materials deposited to form devices that can be taperedphysically and can have continuous and varying indices over a crosssection and axially through a thickness of the material. Such devicesmay have high numerical aperture or étendue or may have low index and orlow numerical aperture or étendue. Some embodiments provide energycoupling, transformation and transport with low or no loss of opticalenergy or power. Some embodiments provide transformation which conservesétendue. Some embodiments provide continuous and slow change,transforming the etendue from the input to the output.

Some embodiments relate to the deposition of amorphous refractorydielectric films and materials that are transparent and provide foroptical films and devices with a wide range of characteristics andapplications. According to some embodiments of the invention, suchmaterial, films and devices can have an extended range of index ofrefraction. The index can, for example, range from MgF to Silica toSapphire (n=about 1.38 to 1.44 to about 1.7) up to that of Titania andtitanium oxide (n of about 3.0 or higher). Mixtures of such oxidesprovide a continuous index over that range through the film, across filmand axially through the film

Previous work has focused on the formation of dense transparent filmswith high indexes (e.g. indexes up to n˜1.7). As such, the followingU.S. Patents and Applications provide background for certain embodimentsof the present invention: U.S. Pat. No. 7,378,356 entitled “Biased PulseDC Reactive Sputter of Oxide Films;” U.S. Pat. No. 7,381,657 entitled“Biased Pulse DC Reactive Sputtering of Oxide Films;” U.S. Pat. No.7,413,998 entitled “Biased Pulse DC Reactive Sputtering of Oxide Films;”U.S. Pat. No. 7,544,276 entitled “Biased Pulsed DC Sputtering of OxideFilms;” U.S. Pat. No. 8,105,466 entitled “Biased Pulse DC ReactiveSputtering of Oxide Films;” U.S. Pat. No. 7,205,662 entitled “DielectricBarrier Films;” U.S. Pat. No. 7,238,628 entitled “Energy Conversion andStorage Films and Devices by Physical Vapor Deposition of Titanium andTitanium Oxides and Sub-Oxides;” U.S. Pat. No. 7,826,702 entitled“Optical Coupling into Highly Uniform Waveguides;” U.S. Pat. No.8,076,005 entitled “Energy Conversion and Storage Films;” U.S. Pat. No.6,884,327 entitled “Mode Size Converter for Planar Waveguide;” U.S. Pat.No. 8,045,832 entitled “Mode Size Converter;” U.S. Pat. No. 6,506,289entitled “Planar Optical Devices and Methods of Manufacture;” U.S. Pat.No. 6,827,826 entitled “Planar Optical Devices and Methods for theirManufacture;” U.S. Pat. No. 6,533,907 entitled “Method of ProducingAmorphous Silicon for Hard Mask and Waveguide Applications;” U.S. Pat.No. 7,469,558 entitled “As-Deposited Planar Optical Waveguides with LowScattering Loss and Methods for their Manufacture;” and U.S. Pat. No.7,205,662 entitled “Dielectric Barrier Layer Films.” Each of the abovecited patents is herein incorporated by reference in their entirety.

Embodiments of the present invention provide for the deposition of oneor more films having vertically and/or lateral graded index ofrefraction over an extended range. Some embodiments provide newprocesses for deposition of materials that are capable of a wide areadeposition at low cost. Devices designed and manufactured according tosome of these embodiments provide efficient and loss-less wave guidestructured devices coupling to and between optical elements with widelyvarying optical aspects such as étendue and index of refraction. Waveguide couplers and transformer devices according to some embodiments ofthe invention can be manufactured by utilization of a high index tomatch the numerical aperture and optical extent of semiconductordevices.

Some embodiments of the invention include, but are not limited to,devices which provide adiabatic or loss-less coupling over a wide rangeof devices with optical aspects having different numerical aperture(NA), optical size and index of refraction. These devices can, forexample, include OLEDs, LEDs, laser diodes (LDs), and mirrors with highNA. In another aspect, some embodiments of the invention relate tocoupling light between devices with the same étendue as well as tocoupling sources and devices having different étendue with adiabatictransfer of light energy. Some embodiments of the invention relate tocoupling high NA devices to low NA devices such as optical fiber,semiconductor devices, planar waveguides, and optical elements withlarge f-number and low NA. In some embodiments, planar thin films andstacked thin films, which are also waveguide devices and which aremanufactured by methods according to some embodiments of this invention,can have vertical and lateral variation in index so as to providewaveguide transport of light and also continuous transformation ofétendue within the waveguide, so as to match NA, optical size and indexas required in combination, into and out of devices including activedevices and layers such as emissive and absorbing semiconducting devicesor phosphor doped layers. Some embodiments of the invention providemethods for manufacturing a coupling device for transforming the étendueand index within the device continuously to provide transport betweendevices with lossless coupling or for coupling to a device and providingselected free space emission different from the coupled source. Thesubject waveguide device can be formed according to embodiments of thepresent invention so as to transform between devices without loss ofoptical through put by conserving étendue where the NA and optical sizeof two coupled devices varies as the inverse.

In some embodiments, devices with different étendue can be coupled withgradual change in étendue by the waveguide coupler transformer. Such acoupler transformer device can also accommodate internally passive andactive elements so as to act upon a selected portion of the guided lightspectrum while coupling the remaining portion of the optical energywithout further loss to free space or an output device. Such a devicecan also be formed by methods according to some embodiments as a planardevice on a wafer can couple one or more integrated optical devices.

Some embodiments of the present invention are directed to methods ofdepositing high index transparent films and materials. Further, someembodiments of the invention are directed to optical devices utilizingthe high index films for the efficient coupling and transformation oflight capacity and flux between optical devices.

Some embodiments are directed to the transformation of light by phosphorand or band absorber material or layers within the waveguide layers anddevices. Further, some embodiments are directed to optical energycollection, concentration, conversion and transport from high NA devicesto low NA devices through a waveguide coupler transformer.

Some embodiments are directed to coupling between optical devices withdifferent numerical aperture and or optical size and different indices,including, for example, semiconductor, mirrors, fiber or other deviceshaving different étendue and or different optical size, numericalaperture or index of refraction.

In some embodiments, films and or devices having in part high index andhigh index contrast or high numerical aperture including waveguidecoupling and transport of coupled light wherein the waveguide transporttransforms the NA and optical size and or the index of refraction over awide range of values from high index materials and or high numericalaperture associated with high étendue to materials, films and deviceshaving low index and/or low numerical aperture and associated lowétendue and differing optical size.

In some embodiments, the deposition of transparent dielectric films withan optical index with a range from magnesium fluoride (n˜1.38) to silica(n˜1.44) to high index, characteristic of semiconductor materials anddevices and titania (n˜3 or higher) can utilize a Bias Pulsed DCprocesses such as that described in U.S. Pat. No. 8,105,466.

In some embodiments, refractory additions including, but not limited to,titanium to oxide films deposited with biased pulsed reactive PVD can beused. Such films, including high index films composed of dielectric andoxide materials as single compounds or as an alloy of one or moredielectric compounds, including Titanium, as described in U.S. Pat. No.7,238,628 can be utilized.

Some embodiments provide a process and method for the formation ofuniform layers having a wide range of index, including an index byaddition of titanium oxide. Such high index layers can have a gradedcomposition through the thickness and also laterally over the substrateor another layer. As such, embodiments of the invention can include thedeposition of a film or films with a wide range of lateral index formingat least one layer of a wave guide structure with a wide range ofétendue or optical extent within a continuous waveguide structure.

In some embodiments, a waveguide device according to some embodimentshas a first étendue and transforms the optical capacity or étendue overa wide range and without loss between a source and another device orfree space, which includes both high NA and low NA as well as highoptical size and low optical size. Some embodiments of the inventionrelate to devices that can be made to couple to a high NA optical deviceat one end, matching the NA and optical size of the source device so asto transport light without loss and then couple to a low NA device,without loss so as to provide an adiabatic coupler transformer.

Embodiments of the invention may include fabrication of a planar couplertransformer that incorporates both macroscopic optical components aswell as thin film microscopic waveguide elements to facilitate coupling,transporting, converting and or transforming light within a continuouswaveguide structure to optical elements with widely different numericalaperture, optical extent and index of refraction. In some embodiments,two or more layers with suitable index of refraction variation bothvertically and laterally to form a light guiding structure to vary bothoptical size and NA. Consequently, a device can be formed having theoptical size and NA of a waveguide device by varying the index ofrefraction laterally and gradually in inverse proportion to conserveétendue in order to efficiently couple light into the waveguide device.

In another aspect the NA and optical size of a waveguide couplertransformer can be gradually varied so as to gradually increase ordecrease the étendue, minimizing the rate of change of opticalthroughput within the waveguide transformer. Etendue can be decreased byeither reducing the optical size of the waveguide at fixed contrast orby increasing the contrast of the waveguide at fixed waveguide size. Inthe last case it is expected that the mode distribution of a waveguidewould increase in mode number. Etendue can also be decreased by doingboth. If the change in etendue is over a distance large with respect tothe wavelength of light reduction in etendue will be adiabatic orlossless.

Some embodiments provide highly efficient devices for coupling highindex and high numerical aperture devices, for example LED, laserdiodes, photodiode receivers and OLEDs or polymer luminaire componentsand assemblies. In applications of planar emissive materials, a layer orlayers having continuous or graded index of refraction, similar andadjacent and increasing in index away from the emissive layer, inanother embodiment of the invention provide a wave guide layer to whichthe light will be directed and by which the light will not be absorbedbut can be directed away from the emissive layer to free space or toadditional high index layers according to this invention for transportor scattering extraction. Some embodiments of the invention enable theintegration of active layers having an index of refraction within thewave guide, such as layers containing phosphor or dopants withelectrical activity or semiconducting layers with continued highefficiency wave guide transport.

Some embodiments are directed to a lateral graded waveguide structurethat provides for the continuous and gradual conversion of étendue to anactive region of the waveguide containing a phosphor, a diode such as aphoto diode or a photo voltaic energy converter or an electricallyactive layer. Such region or layer conveys and/or transforms a portionof the optical energy into and/or out of semiconductor devices embeddedwith the waveguide portion of the planar coupler transformer. Theoptical coupler or transformer converter comprises a region of anintegrated circuit and or discrete component of an integrated passive oractive element of an extended and integrated optoelectronic device orcircuit.

Efficient optical coupling between a high numerical aperture (NA)component (e.g. a photo diode (PD), LED or laser diode (LD), or a wideangle (low f-number) mirror) with or to a low NA component (e.g. awaveguide or distant source such as the sun) depends on matching andoverlap of three things: the optical area; the solid or cone angle ofemission or acceptance; and the index of refraction (n). The product ofthe first two is the étendue (E). The coupling might be by free space,where the solid angle overlap is the important component, or facet tofacet between the two components, where their optical areas should bealigned. It might be for surface or lateral in plane coupling. Sincesemiconductor devices have a high range of index, from as low as 1.7 or1.8 for OLED diodes to 3.4 for amorphous silicon, and optical componentsand films have a low range of index, from 1.44 to ˜1.5 and up to ˜1.7.To date, it has not been possible to match all three aspects of high andlow NA devices, leading to very low coupling efficiency between methodsof optical concentration and transportation and semiconductor devices.

Matching of the small source size of LEDs or LDs with large sources usedfor lighting applications also leads to losses. Étendue can be matchedby the use of lower index materials having a matched contrast resultingin facet reflection with no useful benefit for coupling to low indexdevices. In some embodiments of the present invention, matching tosemiconductor diodes, whether for light extraction or for in-coupling toa photo diode, can be accomplished. In all cases, coupling low NAdevices such as optical fiber or waveguides to high NA, can beaccomplished by interposing one or more lenses to transform some of thesource solid angle into the acceptance angle of the coupled componentand is accompanied by a loss of optical throughput and reflection.

FIG. 1A illustrates conventional coupling of light from an opticalsource 102 to a waveguide 104. As illustrated in FIG. 1A, optical source102 includes active area 106 where light is emitted. Optical waveguide104 includes a core 110 that is surrounded by cladding 104. As is shownin FIG. 1A, the source radiation pattern 112 is too extensive to coupleinto waveguide core 110 and, as a result, there is a lost power portion114 of the source radiation pattern 112 that is not coupled into core110.

FIG. 1A, therefore, illustrates the loss of coupling efficiency due tomismatched NA and solid angle overlap. FIG. 1A illustrates the opticalemission solid angle of source radiation pattern 112 that is typical fora LED. The LED illustrated in FIG. 1A may have NA˜0.7 (resulting from ahalf-angle of ˜44.4 deg.). The mismatch is with both the solidacceptance cone represented by the fiber acceptance angle and theoptical area extent of an optical fiber waveguide, which has an NA˜0.14(resulting from a half angle˜8 deg.).

The mismatch can be evaluated for a high NA LED or LD having an NA up to0.65 for coupling to a lower NA fiber. The emission pattern of the LED,as shown in FIG. 1A, can be given by B(θ,φ)=B₀ cos θ, where B₀ is theradiance along the normal to the radiating surface of active area 106.If A is the normal area of the source and Ω is the solid emission angleof the active area (or source) 106, the Brightness can be given by B₀ AΩ. For a step-index fiber (i.e. where core 110 has a first index andcladding 108 has a second index different from the first index), NA offiber 104 is independent of positions θ and radial distance r and thepower coupled into fiber 104 is given by,P _(coupled) =πr _(c) B ₀ (NA)².The power emitted by an LED source 106 of area A into a hemisphere is2πr_(s) ² B₀, where r_(s) is the radial distance from the source 106.

When r_(c)=r_(s) and NA_(source)=NA_(fiber), the optical throughput iscontinuous and there is no loss or change of étendue. A waveguide corecomprised of 33% alumina with an index of 1.55 in a host glass of silicawith an index of 1.44, which may be formed according to embodiments ofthe present invention, will have an NA of 0.65, matching the LED devicewith respect to solid angle overlap. With equal optical areas, theétendue of such a high NA fiber or waveguide 104 matches that of source106, providing a continuous optical throughput. However due to thedifference in index between source 106, core 110, and the gap betweensource 106 and core 110, reflection at the input facet will cause lossof optical throughput.

Moreover, at the output facet of a coupling device that matches thecontrast and mode field characteristics of a high NA source, there willbe a mismatch again, due to the high contrast, with source size. Withregard to reflection, even with ideal overlap of optical area and solidangle, ‘adiabatic’ or “loss less” coupling cannot be achieved becausefacet reflection will result if the two components being matched have adifferent index. LED and LD devices are comprised of much higher indexmaterials than conventional optical films, with an average index from2.4 in the III-Nitrides to 3.6 or more in GaAs. Even with facet to facetalignment and elimination of an air filled cavity with opticallypolished facets, the reflection is given by

$R = \left( \frac{n_{1} - n}{n_{1} + n} \right)^{2}$where n₁ and n are the average index of the LED and waveguide,respectively. The large loss can be appreciated by the example of a GaAsLED with an index average of 3.6 placed line to line with an opticalfiber with average index 1.48, independent of any mismatch of étendue.The coupled power P_(coupled) is given by (1−R)P_(source). In thepresent example, then, P_(coupled)=0.83 P_(source), resulting in a 17%reflection loss in this coupling.

Fiber coupled LEDs and LDs have been coupled to an index fluid andshaped photonic couplers have been employed for light extraction.However, extraction of light efficiently from a high NA device intoanother device comprised of low index material is not known. This is dueto the Fresnel loss incurred by the use of low index material, even withsuitable contrast and provision of NA. With the addition ofanti-reflection coating, this loss can be reduced. However the need totransform the NA to a lower value remains. Neither is there a continuousoptical element that couples and transforms optical capacity, etc. as awaveguide device.

As was discussed in U.S. Pat. No. 8,045,832 and U.S. Pat. No. 6,884,327,a mode size converter that can help couple light from source 106 tooptical fiber 102 can be provided. FIG. 1B illustrates deposition of amaterial with a lateral taper as described in U.S. Pat. No. 8,045,832and U.S. Pat. No. 6,884,327. As shown in FIG. 1B, a sputter target 124is powered with a power generator 121, which can be a pulsed-dcgenerator or an RF generator. A substrate 125 is placed on a mount table123, which is powered with an RF generator 122 to provide an RF bias tosubstrate 125. A shadow mask 128 is coupled to mount table 123 in orderto partially block substrate 125 from sputter target 124. As shown inFIG. 1B, material is sputtered from sputter target 124 and is depositedto form material layer 126 on substrate 125. Because of shadow mask 128,taper 127 is formed in material layer 126. A layer of material 129 isalso deposited on shadow mask 129. The deposition occurs within vacuumchamber 128 and sputtered material 130 is drawn to substrate 125 in theprocess.

FIG. 1C illustrates a mode-size converter deposited according to theprocess illustrated in FIG. 1B. FIG. 1C illustrates device 131 formedwith two shadow masks 209. Further, an additional layer 130, which maybe a cladding layer or may be a passive core layer, may be depositedover substrate 125 prior to deposition of layer 126 with tapers 127,which may be a core of a planar waveguide.

FIG. 1D illustrates an alloy film of 92% SiO2 and 8% Al2O3 depositedthrough a shadow mask according to the process described above. FIG. 1Dshows taper 127 of an E¹⁸/cm³ Er⁺³ ion doped film in ambient light,which extends from layer 126 across taper 127 indicated the regionindicated by the optical fringes to uncovered layer 130. Such taperedregions having an extent of gradual taper over a distance of more than10 mm, as illustrated in ruler 142, from full thickness to the uncoatedportion of layer 130 on the left hand side to the full thickness ofdeposited layer 126 on the right hand side.

FIGS. 2A and 2B show an active device 131 according to the processesdescribed above that performs a mode size conversion from 1060 opticalfiber 202 into a similar sized passive waveguide layer 130 with modesize conversion into the higher index tapered film 126. Actual loss wasmeasured in an actual device as shown in FIG. 2A showing the pump fibercoupled 1350 nm pump light coupled into the passive waveguide, withlower NA and large mode size picture taken with cleaved device. Also,green fluorescence and small mode size from higher NA Erbium ion doped92/8% Aluminosilicate film (92% Al₂O₃ and 8% SiO₂) forming the core of aplanar optical amplifier formed as layer 210. As shown in FIG. 2A, light206 is a cross section of fiber 202 and light 208 is from a crosssection of amplifier layer 126. Mode size conversion is accomplishedwith taper 127 in amplifier layer 126. As shown in FIG. 2B, taperedlayer 126 is deposited over core 210 and prior to deposition of acladding layer.

FIGS. 2C through 2F illustrate another embodiment of Mode Size Converterdevice 204. In this case, the tapered layer 126 is deposited over alower cladding layer 214 and then core layer 210 is deposited overtapered layer 126 and an upper cladding layer 212 is deposited over corelayer 210. FIG. 2C illustrates a top view of device 204. As shown inFIG. 2C, light from fiber 202 is coupled into core layer 210. Taperedlayer 126 is formed on core layer 210 and an upper cladding layer 212 isprovided. FIG. 2D illustrates a side view of device 204. As shown inFIG. 2D, tapered layer 126 can be formed on a lower cladding layer 214and core layer deposited on tapered layer 210. A top cladding layer 212is then deposited on core layer 210. FIG. 2E illustrates a cross sectionof device 204 in a region of device 204 that does not include taperedlayer 126. FIG. 2F illustrates a cross section of device 204 in a regionof device 204 that includes tapered layer 126.

FIG. 3 is a rendering of a planar waveguide coupler 304 with an LED chip302. FIG. 3 shows coupling from a lateral facet 306 of the LED proximateto and aligned with the core of the NA matched waveguide 308 of thecoupler transformer portion. The coupler transformer portion couples andtransforms the optical throughput into the macroscopic substrate 310with a lower NA and a low angular far field emission formed bymacroscopic waveguide elements. Light propagated in layer 308 undergoesa mode-sized expansion and expands into light 301A in substrate 310 andexits chip 302 as light 310 b. As a result, light is more efficientlycoupled from LED 302 out of waveguide 304.

FIGS. 4A through 4F illustrate an apparatus 400 for providing a shadowmask 402 over a wafer 406. As shown in FIG. 4A, a shadow mask 402 withopenings 408 can be mounted to a fixture 404 that itself is mounted to awafer 406. Openings 408 in shadow mask 402 provide for masking thatresults in a tapered deposition as discussed above. As is further shownin FIG. 4A, ball positioning array of sockets 410 and slot 412 can beused to position and register mask 400 to wafer 404.

FIGS. 4B through 4F illustrate apparatus 400 in more detail. Inparticular, FIG. 4B illustrates shadow mask 402 with openings 408.Aligners 410 and 412, which may be balls or dents, can be used foralignment of shadow mask 402 with fixture 404. As discussed above,sockets 410 is a ball positioning array and slot 412 can receive a pin.FIG. 4C illustrates fixture 404. Fixture 404 has aligners a ball 414 andpin 416 to align with shadow mask 402 at socket 410 and slot 412,respectively, and a preload flex finger 420. Pin 416 can be a linearguide pin for guidance of mask 400 over wafer according to the positionof ball 414 in sockets 410. FIG. 4D shows the combination of shadow mask402 with fixture 404 and a wafer 406. FIG. 4E illustrates the assembledapparatus 400, including wafer 406. FIG. 4F illustrates a cross sectionof apparatus 400 as shown in FIG. 4E across the direction AA. In someembodiments, balls and detents are shown as a method of lateraldisplacement positioning of the mask over the substrate so as to providelateral overlapping coating over lateral portions of the substrate insequence.

Apparatus 400 can be of any convenient size. As a single example, whichis only intended to be illustrative and is not intended to be limiting,openings 408 can be 5.0 mm wide and separated by 10.0 mm. Further,shadow mask 408 can have an outer diameter of 274.3 mm. Fixture 404 canhave an inner diameter of 150.0 mm and an outer diameter of 279.4 mm.The lengths, number and spacing of slots 408 can be determined by thenumber of individual layers to be deposited.

The above discussion demonstrates how a physical taper can be formed ina layer. FIGS. 5A, 5B, and 5C illustrate a deposition chamber 500 fordeposition of materials. FIG. 5A illustrates the top 502 of depositionchamber 500, which includes plate 508 into which multiple individualtargets 504 are mounted. Targets 504-1, 504-2, 504-3, and 504-4 areillustrated but there may be any number of targets 504 mounted in plate508. As illustrated in FIG. 5A, individual targets 504 may beappropriately shaped and spaced around plate 508 and each coupled to anindividual power source 506 (power sources 506-1, 506-2, 506-3, and506-4 are illustrated). Each of targets 504 may be chosen appropriatelyfor deposition of different material layers, for example material layersof differing indices of refraction. In some embodiments of the presentinvention, multiple ones of targets 504 may be powered by thecorresponding one or more power sources 506 during deposition. Forexample, two individual targets 504 can be powered by correspondingpower supplies 506 during deposition in order to form an alloyed layermaterial.

FIG. 5B illustrates a rotating table 510 that is mounted opposite top502 in deposition chamber 500. Table 510 can include mounts for multiplewafers 512, of which wafers 512-1, 512-2, 512-3, and 512-4 areillustrated. In some embodiments, each of the multiple wafers 512 may becoupled to a separate power source 514 to provide bias, however in theexample illustrated in FIG. 5B a single power source 514 is illustrated.Wafers 512 are mounted on rotating table 510. Rotating table 510 isrotated at a particular rate during the deposition process.

FIG. 5C illustrates a cross section of deposition chamber 500 where oneof sources 504 is aligned with one of wafers 512 for a deposition ofmaterial on wafer 512 when power supplies 506 and 514 are activated.Power sources 506 and 514 are chosen appropriately for the particulardeposition process and, for example, can be pulsed-DC, DC, or RFsources. Rotational speed of table 510 along with the power applied bypower supplies 506 and 514 can be set accordingly for a particulardeposition of materials, which can result in an alloyed layer ofmaterials as discussed further below. Bias power supply 514 can be usedas an etch bias plasma to densify and mix deposition materials frommultiple targets 504 to create the deposited alloyed material, which maybe amorphous materials.

FIG. 5D, shows the Tango Systems AXcela PVD sputter system 500 with softclean chamber 520 and two process chambers 500 on either side. Processchambers 500 are described above with respect to FIGS. 5A-5C. FIG. 5Eshows a process chamber 500 of the system illustrated in FIG. 5D. Asshown in chamber 500 illustrated in FIG. 5E, plate 508 includes openings530 into which targets 504 are inserted. As shown in FIG. 5E, targets504 can be described as a triangular “delta” sputter source targets,which for purposes of illustration are removed from plate 508 in FIG.5E. Through opening 530, rotatable table 510 is illustrated along withmounts 532 on which wafers 512 are positioned. Table 510 can bedescribed as a ‘wrap around inline’ rotation table. Deposition ofmaterial layers from each of the sputter source targets 504 can be madeuniform across each of wafers 512. Operation of two or more of sputtersource targets 504 simultaneously can provide a film of uniformcomposition through the film thickness and across each of wafers 512.Variation of deposition parameters such as power in each of sputtersource targets 504 can provide variation of material properties such asindex of refraction through the thickness. The vertical composition canbe changed uniformly provided that the change in deposition parametersis slower than the mixing of layers from source targets 504.

FIG. 5F illustrates two sequential substrate positions of mounts 532 onrotating table 510 underneath opening 530 where sputter target 504 ispositioned in process chamber 500. A wafer 512 positioned on mounts 532can be rotated under sputter target 504 as part of a sequentialdepositions of material.

FIG. 5G shows the triangular ‘Delta’ sputter source target 504. Asillustrated, target 504 includes a metallic target material 536 mountedon a backing 534. Target 504 is shaped to be mounted into opening 530with target material 536 facing towards table 510.

FIG. 5H shows rotating table 510 in process chamber 500. As illustrated,mounts 532 are positioned around table 510 so that wafers on mounts 532can be rotated under targets 504.

FIG. 5I illustrates a process 550 for depositing alloyed materialsaccording to some embodiments of the present invention. As shown in FIG.5I, wafers are loaded into cleaning chamber 520. Cleaning chamber 520 isin vacuum and provides an etch step to clean the surface of the wafersin wafer preparation step 554. Wafers are transferred to rotating table510 in step 556. Wafers 512 are positioned on mounts 532 on rotatingtable 510. Deposition chamber 500 is already evacuated and, in step 558,process gas is flowed for the deposition. In step 560, a particularrotation speed is set. In step 562, one or more of targets 504 ispowered to provide deposition material. In step 564, a bias power is setand applied to wafers 512. In step 566, a determination of whether thematerial layer is deposited as desired is made. If not, then process 550returns to process gas flow step 558. During deposition, process gasflow, rotational speed, target power, and bias power may be variedstepwise or continuously to alter the material composition and/orthickness. of the material layer. If, in step 566, the material layer isdetermined to have been completely deposited, in step 568 it isdetermined if an additional material layer is to be deposited. If so,process 550 returns to step 558. In a second material layer, differenttargets 504, powers, gas flows, rotational speeds, and depositionparameters may be adjusted as is suitable. Any number of material layersmay be deposited. If all of the material layers have been deposited,then process 550 proceeds to step 570 where wafers 512 are unloaded fromthe deposition system 500.

According to some embodiments, a plurality of film layers can bedeposited according to process 550 that corresponds to a planarwaveguide structure. These layers can be deposited continuously or in astep index fashion forming a lower index layer upon a higher indexlayer. With a lower index substrate two composite films can be depositedas either a step index or graded index composite films forming with thesubstrate a wave guide structure. The contrast ratio of the high and lowlayers deposited from a plurality of sputter sources determines theassociated numerical aperture, the average index and also the associatedbound mode volume can be selected by rule of mixture of transparentoxides as composite layers along with the thickness of the compositewave guide layers so as to provide a wave guiding structure in the planeof the substrate.

The thickness of a film, or film portion, deposited according to process550 can include contributions from a plurality of sources that areco-sputtered and may be proportional to the sputter power applied toeach individual target 504 and inversely proportional to the relativerotation speed between target 504 and substrate wafer 512. A film with aplurality of film layers will be formed if substrate bias is notapplied. With higher rotational speed or lower sputter power, layersformed in sequence as the substrate passes under each of the sputtertargets in sequence will form a thinner layered composite film. If thelayer thickness provided is less than about a quarter wavelengththickness of light in the film, the light will be governed by an averageeffective index. If the films are deposited with a substrate bias, thelayers will be mixed and densified by the bias ion current. If the filmlayers from the discrete sputter sources target 504 are less inthickness than the bias effected zone, often taken as about three to tenmonolayers, they will be mixed and densified and form a continuous alloywith a composite composition.

A rotary inline sputter system 500 as discussed above with a pluralityof substrate wafers 512 and a plurality of sputter source targets 504with target material or materials utilized for co-sputtering can formfilms or layers of uniform composite composition from multiple sourceshaving the properties of a portion of a wave guide. A material layer canbe deposited as a step film of constant composite composition andproperties or a film having a graded or continuously changing thicknessand index of refraction through thickness by variation of the powerapplied to the sputter source targets 504 which have a uniform filmthickness over the substrate wafer 512. A rotary inline system 500provides continuous deposition from one or more target materials on allsubstrates at preselected and varied rates of deposition by process 550so as to form a continuous film having a constant or continuouslyvarying composition and index. By deposition of less than a monolayer orby deposition of less than the thickness which is mixed by forwardscattering into the film by the bias ion current (power supply 516) andthe coupled ion current impinging on the accumulating film, a densetransparent film can be formed. Such a film or layer composition iscontinuous or layered depending on the power applied to one or more ofthe sputter sources.

Films were deposited on 300 mm wafers with the 300 mm Axcela Magnetronthree cathode rotary inline sputter system at Tango Systems, 2363 BeringDrive, San Jose, Calif. using a process such as that illustrated byprocess 550. Substrates to be coated were placed in the vacuum chamber500 and a vacuum was attained of better than E-7 Torr. Oxide films weredeposited using biased pulsed DC reactive sputtering (i.e. PowerSupplies 506 are pulsed DC and power supply 514 is an RF supply) withthe Axcela, rotary inline sputter system 500. Metallic targets 504included one each of Titanium, Aluminum, Hafnium and Silicon targetmaterials. The metallic targets 504 were sputtered at 3 kW Pulsed DCpower with a pulse return time of 2.6 us and a pulse frequency of 150KHz. The bias power was applied through a matching network to convey thepower to the back side of the substrate wafer 512 and showed less than 5Volts reflected power. The applied bias power was 400 W at 13.56 MHz.Rotation of table 510 was set at 10 rpm. The time of deposition was 1500sec or 25 minutes for all except Run #3, which was 1200 sec. The numberof passes under one or more source targets 504 for the nominal 300 Angfilm in 25 minutes was 250 passes with a net thickness of 1.2 Ang perpass which is essentially half a monolayer, assuring complete mixing ofthe material due to the bias and elimination of deflects such as singlepoint vacancies on a sub atomic scale. The duel sputtered films,deposited at essentially half the rate of the pure films were mixedtwice as well with the substrate passing under both source targets 504on each rotation for about a quarter of a monolayer deposition andmixing. The ratio of Argon to O2 in SCCM of process gas was between15/25 to 20/40. Run #4 was performed at a ratio of 10/30. The oxidethickness was measured by an lab optical thickness tool initially and isapproximate. The index of refraction for several films is illustrated inFIGS. 12A through 12D.

Refractive Extinction index at coefficient at Thickness RUN Material 450nm 450 nm (nm) 1 TiOx 2.86 <1.0 × 10⁻⁵ 44 2 HfOx 1.67 <1.0 × 10⁻⁵ 70 3AlOx 1.63 ~1.0 × 10⁻⁵ 54 4 TiHfOx 1.91 <1.0 × 10⁻⁵ 115

FIGS. 12 A, 12B, 12C, and 12D show the ellipsometer data for the opticalindex and extinction values for films made according to some embodimentsof the present invention. FIG. 12A illustrates the index of refractionfor a film of TiO_(x) for wavelengths of light from 1 micron to 0.3microns and shows a k value below detection near 350 nm, which is aboutE-5 indicating very high transparency.

FIG. 12B is for hafnium oxide for the same range with undetectable kvalue throughout. FIG. 12C is for aluminum oxide showing a k value frombelow 2E-5 to less than 1.2E-4. FIG. 12D is for a mixture of titaniumoxide and hafnium oxide sputter deposited as a uniform amorphous alloyas described in the present invention.

In Run #4, two source targets 504 were run simultaneously at 3 kW each.The total thickness of run #4 is the sum of runs #1 and #2, that is 115vs. 114, better than 1%. However a rule of mixture from thickness of thefilm thickness, ˜38.6% TiO₂ and 61.4% HfO₂ gives a total weighted indexof 2.12 from the two measured index values at 450 nm, higher than themeasured index of the mixture of 1.91 measured. An index below the ruleof mixture is well known and can be referred to as “parabolic” but anactual shape for the trend of alloy index for a mixed oxide must bemeasured in application. But it is clear that a mixture of the twooxides provided by selection of a suitable power ratio can be achievedwith the compounding of the high index amorphous TiO2 oxide fraction forthe 450 nm LED MQW planar waveguide coupler core and cladding layers ofapproximately n=2.4 for p and n GaN and n=2.6 for the Indium doped GaNlight emitting region. Measured and fit index as a function of the powerratio of TiO2 and HfO2 is shown in FIG. 36 for three wavelengths, 400nm, 450 nm and 500 nm, which are illustrated from top to bottom in FIG.36.

Film deposition for a waveguide coupler transformer for use at 450 nmwith an LED or Laser diode is shown in the following table using process550 according to some embodiments of the present invention. Thewaveguide coupler has a fast output angle of ˜about 40 degree, an NA ofabout 0.624884 and an average index of about 2.59. The coupler alsoexhibits transformation and out coupling to an optical fiber or freespace with an NA of about 0.12, Deposition is carried out using themeasured and fit tabular index data shown graphically in FIG. 36 forconstant power deposition of the TiO₂ at 4 kW pulsed DC power asindicated in the table below.

Film deposition example at 4 kW TiOx/HfOx HfO2/TiO2 index at HfO2 halfPower ratio 450 nm NA Watts angle 0 2.7544 0.932581 0 68.84074 0.016952.59172 0.624884 67.8 38.67365 0.0339 2.51526 0.470409 135.6 28.060870.05085 2.47088 0.392229 203.4 23.09328 0.0678 2.43955 0.342907 271.220.05408 0.08475 2.41533 0.30809 339 17.94418 0.10169 2.3956 0.281951406.76 16.37667 0.11864 2.37895 0.261174 474.56 15.13973 0.13559 2.364570.244454 542.36 14.14956 0.15254 2.3519 0.230475 610.16 13.32506 0.169492.34058 0.218488 677.96 12.62024 0.18644 2.33036 0.208209 745.7612.01742 0.20339 2.32104 0.199156 813.56 11.48758 0.22034 2.312480.191225 881.36 11.02428 0.23729 2.30456 0.18416 949.16 10.61216 0.254242.29719 0.177657 1016.96 10.23331 0.27119 2.29031 0.171898 1084.769.898217 0.28814 2.28385 0.166674 1152.56 9.594491 0.30508 2.277760.161744 1220.32 9.308149 0.32203 2.27201 0.157274 1288.12 9.0487220.33898 2.26656 0.153297 1355.92 8.818039 0.35593 2.26137 0.1492411423.72 8.58293 0.37288 2.25644 0.145872 1491.52 8.387753 0.389832.25172 0.142444 1559.32 8.189271 0.40678 2.24721 0.139435 1627.128.015147 0.42373 2.24288 0.136377 1694.92 7.838252 0.44068 2.238730.133768 1762.72 7.687377 0.45763 2.23473 0.131121 1830.52 7.5343490.47458 2.23088 0.128605 1898.32 7.389015 0.49153 2.22717 0.1262291966.12 7.251725 0.50847 2.22359 0.124176 2033.88 7.133172 0.525422.22012 0.121916 2101.68 7.00271 0.54237 2.21677 0.119994 2169.486.891728 0.55932 2.21352 0.118048 2237.28 6.779442 0.57627 2.210370.116077 2305.08 6.66577 0.59322 2.20732 0.114467 2372.88 6.5728750.61017 2.20435 0.11284 2440.68 6.479036 0.62712 2.20146 0.1111952508.48 6.384202 0.64407 2.19865 0.109732 2576.28 6.299862 0.661022.19591 0.108052 2644.08 6.203016 0.67797 2.19325 0.106762 2711.886.128697 0.69492 2.19065 0.105253 2779.68 6.041769 0.71186 2.188120.104149 2847.44 5.978114 0.72881 2.18564 0.102611 2915.24 5.8895320.74576 2.18323 0.1017 2983.04 5.837073 0.76271 2.18086 0.100351 3050.845.759358 0.77966 2.17855 0.098987 3118.64 5.680836 0.79661 2.17630.098053 3186.44 5.627056 0.81356 2.17409 0.097113 3254.24 5.5729210.83051 2.17192 0.09594 3322.04 5.505414 0.84746 2.1698 0.094984 3389.845.450424 0.86441 2.16772 0.093791 3457.64 5.38176 0.88136 2.165690.093052 3525.44 5.339237 0.89831 2.16369 0.092075 3593.24 5.2829970.91525 2.16173 0.09109 3661 5.226307 0.9322 2.15981 0.090336 3728.85.182911 0.94915 2.15792 0.089336 3796.6 5.125396 0.9661 2.156070.088814 3864.4 5.095362

FIG. 12E is a scanning electron microscope image of a cross section of atitanium dioxide (TiO₂) coating 1200 on a substrate 1206 containing anamorphous phase or layer portion 1204 and a crystalline layer portion1202. The material in FIG. 12E is a biased pulsed-DC deposited TiO₂ atsimilar powers as described above. Amorphous portion 1204 is clearlyseen between substrate 1206 and crystalline layer 1202 as a smooth graylayer with a sharp lower interface and a diffuse upper interface havingvariable thickness shading into the crystalline layer 1202. Thecrystalline phase 1202 was induced by increasing the depositiontemperature and formed during deposition without crystallization of theamorphous layer 1204 deposited prior to heating by the heat ofdeposition. The inset 1208 shows a selected area diffraction in whichthe center disk region indicates the presence of amorphous phase 1204,and stress elongated point group patterns appear as outer spots arrangedon rings associated with the crystalline phase 1202. Substratetemperature control below about 150-180 deg. C. maintains deposition ofthe amorphous phase 1204 with demonstrated optical transparency. PureTiO₂, will provide the maximum acceptance angle and solid angle for edgeemission or in coupling as a layer on a plate of lower index dielectric,such as glass. The high index film maximizes the solid angle acceptanceof the surface of the coated plate or glass, providing maximumcollection of diffuse light which is transported to the edge of thestructure.

FIG. 12F shows n and k data for two films of titanium dioxide depositedat 4 kW pulsed DC power from a metal target by reactive depositionaccording to some embodiments of the present invention. TiO2 films weresputtered at 3 kW Pulsed DC power at a rotational rate of 10 rpm on 300mm borosilicate wafers with and without 500 W of 13.56 MHz RF bias. Theellipsometer data in FIG. 12F shows the effect of the RF bias whichincreases the index over the visible range, due in part to the formationof a higher density film which is in turn due to the ion bombardmenteffect of the RF bias. In addition the RF bias decreases the k orextinction value of the film, making it suitable for low loss waveguidefabrication. The decrease in the k value is due in part to theelimination of the columnar structure familiar to thin refractory films.The application of RF bias in the amount of 500 W can be seen to haveraised the index and lowered the k value of the amorphous films acrossthe measured range, providing a high index film with very low k value.This represents the film material that is utilized to achieve mixtureswith other oxides as demonstrated here with different and varying nvalues and low k values.

FIG. 12G shows ellipsometry data n and k, for two amorphous alloy filmsof TiHfO_(x) deposited with 500 W substrate bias at 13.56 MHz andcompounds of Titanium oxide and Hafnium oxide according to someembodiments of the present invention. Each film has a different pulsedDC sputter power in kW as shown. The TiO₂ portion of the films wasdeposited at 4 kW. The film with the portion of HfO₂ deposited at 0.7 kWhas a higher index than the film with HfO2 deposited at 3 kW by an indexdifference, dn˜0.2 in the visible, showing a wide range of high index bymixture, between the index of the two pure compounded films. The filmwith the higher power portion of HfO2 has a lower k value, showing thevery large decrease in extinction available with increasing addition ofthe Hafnium oxide.

FIG. 12H shows ellipsometry data n and k for films of HfO_(x) and showsthe increase in index for a HfO_(x) film sputter deposited with 500 W RFbias compared to the same film deposited without RF bias. Both filmshave k values below detection over the measured range.

FIG. 12I shows ellipsometry data indicating the range of index for fourfilms: TiO₂, an alloy of TiO₂ and HfO₂; HfO₂; and Al₂O₃, each depositedaccording to embodiments of the present invention. These films areavailable to form transparent alloyed optical films alloys from thelowest index to the highest index of the pure films as well as formingtransparent films and devices continuously graded through thickness aswell as including a laterally graded index.

FIG. 12J shows the extinction value for three films according toembodiments of the present invention. These films may be utilized toprovide transparent, low absorption layers and devices over the rangeshown and by extrapolation in the infrared and UV. Note that the pureHfO₂ value is below E-8 across the range.

FIG. 12K shows the index of a range of TiO₂ films alloyed with HfO₂ overa range of sputter power at 400 nm. FIG. 12L shows the index of a rangeof TiO₂ films alloyed with HfO₂ over a range of sputter power at 450 nm.As indicated, the index of refraction can be controlled by varying thesputter power of deposition. As indicated in FIGS. 12K and 12L, atmultiple wavelengths a desired index can be formed by the selection ofpower ratios to provide the selected composition and index. By varyingthe power ratio continuously across a selected range index, particularpre-defined shape of the index of refraction with thickness can bedeposited to provide a continuously grated or shaped index.

In addition to a series of individual layers as discussed above,individual layers with differing shadow mask positioning can bedeposited. Individual layers of continuously varying composition can bedeposited in each position of shadow mask 400 according to process 440.Additionally, shadow mask 400 can be moved across the wafer insubstantially a continuous procedure, as discussed below.

FIGS. 6A and 6B illustrate coating portions transmitted through alaterally moving shadow mask 400 sequentially as the mask 400 is movedover a substrate during deposition Deposition can be performed accordingto process 550. As illustrated in FIG. 6A, coatings 601-1 through 601-nare sequentially deposited and can form a converter layer. FIG. 6Billustrates the results of the sequential deposition. A lateral portionof a deposited film at each of a number of positions of the shadow mask400 is formed as separate coating thicknesses 601-1 through 601-narriving from bottom left to top right in time through the shadow maskpositioned at different lateral positions. As illustrated in FIG. 6B,the resulting film is shown as a cumulative coating buildup laterallyformed from coatings 601. The thickness of the layer is determined bythe rate of deposition of each portion at each position and the timeduration of the substrate beneath the position of the shadow mask. Insome embodiments, each coating layer 601 of the film is provided amaterial composition so as to provide a continuous lateral change inthickness, composition and, or index of refraction through film 600.

FIG. 6C shows the cross section of a waveguide device 620 with layers601-1 through 601-n accumulated through lateral movement of a shadowmask 400 with deposition of a film with varying index according to someembodiments of the present invention. The deposited layer forms a core636 of a waveguide having an input light solid angle 630 with a smalloptical area, high index and high contrast to the upper and lowercladding materials with a large half angle as illustrated. The corelayer 636 (formed by layers 601), from left to right, represent lateralportions of the film having lower index contrast to the cladding andtherefor a larger optical size for the guided light, left to right. Thelight capacity or étendue of waveguide 636 is shown such that the indexof the deposited core layers 601 on the far right are just above, equalto and then just under the index of substrate 634. The optical capacityis formed into the substrate which has a lower NA with respect to itsupper and lower material to provide a small contrast, small NA and smallhalf angle as well as a large optical size at the output facet asillustrated by output 632. Such a device can be formed according to someembodiments so as to conserve the étendue of the source, transformingsolid angle ratio into optical size ratio. It can be formed so as togradually or adiabatically increase or decrease the étendue.

FIG. 7 shows a cross section of a device 700 having layers formedaccording to some embodiments of the present invention. As illustratedin FIG. 7, device 700 includes a substrate 702, cladding 704, and core706 formed as a varying index series of layers 601 as illustrated inFIG. 6B. The waveguide device 700 has a first optical size, area A1 andfirst index n1, left, gradually changing into a second area A2 and indexn2, right. The optical capacity remains centered in the film and a firstétendue, E1=2πA1(1−cos Φ₁) is transformed and is equal to the secondétendue, E2=2πA2(1−cos Φ₂). Case 2 is that the étendue E1 does not equalE2 but is transformed gradually and adiabatically to the componentelement values of E2 through the lateral graded index.

FIG. 8 shows the installation design of the shadow mask position ‘clock’drives 702 in the AXcela rotary inline process chamber. As illustratedin FIG. 8, mask 400 covers a wafer 512 mounted on table 510. Each clockdrive 702 has a shadow mask 400 and a substrate wafer 512 to be coated.Each clock drive 702 has a drive gear 704 and drive screw 706 to utilizethe rotational motion of table 510 to move the shadow mask 400laterally. In some embodiments, drive gear 704 and drive screw 706 canalso be referred to as a cogged wheel and a lead screw, respectively,and drive movement of shadow mask 400 on rotary table 510 in awrap-around inline rotary coating process within a vacuum chamber. Asillustrated in FIG. 8, a pin 708, whose location is fixed on chamber500, is used to rotate cogged wheel 704 a portion of a rotation eachtime wheel 704 of clock drive 702 passes the fixed position of pin 708.As indicated, pin 708 can be rotated to move cogwheel 704 eitherclockwise or counterclockwise, depending on position, or disengaged toleave mask 400 stationary. Advancing cogged wheel 704, through leaddrive screw 706, advances shadow mask 400 across substrate wafer 512laterally a portion of the amount of the pitch of drive screw 706.

FIGS. 9A and 9B are photos showing some aspects of clock drive 702 andshadow mask 400 driven by rotation of cogged wheel 704 by chamber pin708. In some embodiments, pin 708 can be withdrawn and inserted assubstrate table 510 rotates and mask 400 drives passed the pin positionto turn cogged wheel 704 and move mask 400 or removed, to leave mask 400in a position so as to accumulate additional coating through havingshadow mask 400 at its current position.

FIG. 10 is an illustration showing the drive pin 708 engaged with thecogged wheel 704. As table 510 rotates, cogged wheel 704 captures pin708 and rotates. Screw 706 is then driven by cogged wheel 704 and movesshadow mask 400. The amount of rotation of screw 706 by cogged wheel 704is determined by the number of receivers on cogged wheel 704. The amountof movement of shadow mask 400 depends on the amount of rotation ofcogged wheel 704, the pitch of screw 706, and the coupling between screw706 and shadow mask 400.

In addition to a lateral movement of mask 400, mask 400 can also belifted. FIG. 11 shows a lift mechanism 1101 activated mechanically by anarm 1103 that extends through a vacuum seal in vacuum chamber 500 so asto lift shadow mask 400 vertically away from wafer 512 at the load,unload position opposite the gate valve 1105 for unloading of coatedsubstrates and loading of substrates to be coated.

FIG. 13 illustrates a process 1300 that uses a clock drive 702 accordingto embodiments of the present invention. As illustrated in FIG. 13,process 1300 is substantially the same as is process 550 illustrated inFIG. 5I. However, after step 1302, clock drive 702 may be engaged(either clockwise or counterclockwise) to rotate cogwheel 708 ordisengaged. Further, after deposition of one layer is completed asdetermined in step 566, clock drive 702 may be engaged or disengaged torotate cogwheel 708 prior to deposition of a second material layer.Further, a step 1306 can be performed before the wafers are unloaded instep 570. Step 1306 can reposition shadow mask 400. One skilled in theart will recognize that process 1300, as is process 550, is exemplaryonly. Processes can be varied accordingly to accomplish particularmaterial layer depositions

FIG. 14 illustrates the cross section of a coating on a substrate 1410.Coating portion layers 1406-1 through 1406-n (collectively 1406) to formlayer 1404 followed by layers 1408-1 through 1408-m (collectively 1408)to form material layer 1402. Layers 1406-1 through 1406-n formsequential portions of a continuous deposition accomplished by coatingthrough the lateral moving shadow mask 400 according to process 1300 andconstitute a first coating layer 1404, which results from coating byscanning the shadow mask 400 in a first direction. In some embodimentsof the invention portions 1406-1 through 1406-8 have a continuouslateral variation of composition and associated continuous variation ofthe index of refraction. Coating portions 1408-1 through 1408-mconstitute a second coating layer 1402 and are deposited over the top ofthe first layer 1404 in a second direction, which in this diagram isopposite the first direction. Some embodiments comprise a continuousrange of lateral variation of composition and index of the second layer1402. In some embodiments the average index of the second layer 1402 canbe lower than the average index of the first layer 1404. In someembodiments all the index of the portions of the second layer 1402 havean index less than any of the layers of the lower layer 1404, forming alight guiding structure with an NA that varies laterally. FIG. 15 showsa core wave guide series of portions representing stages of a continuousprocess of forming a first layer 1502 deposited on substrate 1503 suchthat the thickness of the coating is also continuously increased fromleft to right. Layer 1501 is a second layer deposited over the firstlayer and has a single index of refraction and thickness and forms alight guiding cladding on the higher index first layer 1502. When facetsare formed at a distance from each end, a light guiding device with asmall optical facet on the left hand facet and a large optical facet atthe right hand facet with a continuous change or transformation of theoptical size from on to the other facet.

FIG. 16 illustrates the cross section of a first layer 1602 of constantthickness with gradually varying index of refraction under a secondlayer 1591 so as to form a light guiding structure. Forming facets ofequal optical size but varying NA and étendue can be formed.

FIG. 17 shows layers of a device for in-coupling or out-coupling light,both specular and diffuse. Layer 1705 can be a solid structure oftransparent material such as glass or plastic. Layer 1700 can be anemissive region or an adjacent region wherein diffuse light wouldimpinge. Layer 1702 can be an amorphous transparent layer according tosome embodiments of the present invention having an index of refractionequal or greater than that of emissive layer 1700. The index of layer1702 increases in index away from layer 1700 and toward layer 1704.Light incident on layer 1702 will be guided away from layer 1700 andconcentrated in the higher index region of layer 1702. In someembodiments, layer 1704 and/or 1706 are crystalline layers, which willscatter the diffuse light. Light entering layer 1704 from layer 1702will either be scattered back into layer 1702 or scattered in theopposite direction into layer 1705. Light scattered back to layer 1702will be transported in layer 1702 higher index portion until it is againscattered by layer 1704 until the preponderance of the light transportedin the layer 1702 will have been scattered into and through transparentstructure 1705. Likewise, light impinging layer 1704 from structurelayer 1705 will be scattered out of layer 1704 or scattered back throughlayer 1705. The light fraction reaching the high index portion of layer1702 can be captured and transported until scattered by layer 1704through layer 1705 and scattered out of structure 1710. In someembodiments mirrors or coatings 1708 reflect light which cycles asdescribed and is emitted through layer 1704 from device 1710.

FIG. 18 shows that about 50% of the light emitted by an OLED structureis trapped by the waveguide formed between the OLED and the glass. See,e.g., K. Saxena, D. S. Mehta, V. K. Rai, R. Srivastava, G. Chauhan, M.N. Kamalasanan˜J. Lumin. 128 (2008) 525. Improvement in the out-couplingof the light can, according to some embodiments of the presentinvention, be achieved by interposition of a graded layer having theindex of the transparent oxide and increasing to a higher index eitheras a step index or a graded increase through the thickness of theinterposed film. That structure can provide a grin or waveguidestructure that is transparent and will transport the emitted lightlaterally. Additionally the glass may be roughened or patterned prior todeposition of such a graded or stepped index layer.

FIG. 19 shows a device according to some embodiments of the presentinvention. As shown in FIG. 19, layers 1901 through 1902 are depositedon substrate 1910 according to process 1300 with a lateral indexgradient, which may be from high to low index. Cladding layer 1908 isdeposited over layers 1901 through 1902 and has an index correspondingto lower cladding 1912. As is further illustrated, layer 1906, which caninclude a dopant such as a phosphor or be semiconductor material formedthrough a mask, can be deposited adjacent to or part of the core of thewaveguide under cladding layer 1908 and over layers 1901 through 1902.The index of layer 1906 can be chosen such that a portion of lightcoupled through area 1904 travels through layer 1906, excitingfluorescence and stimulating emission. Cutting and polishing of thelight guiding structure at facets 1903 and 1905 forms facets and providea planar waveguide coupler transformer with an optical area at facet1903 formed with core layer 1901 and an optical area at facet 1905formed with the cladding 1908. Light coupled into the device at facet1903 will propagate through the waveguide with a portion passing throughlayer 1906 depending on the index contrast between layer 1906 and thelayers 1901 through 1902. The light will be guided by mode sizeconversion out of layers 1901 through 1902 and emerge from facet 1905with the NA determined by the contrast between layers 1901 through 1902with the fluorescent light from layer 1906 as well as a portion of thelight incident on and transmitted from facet 1903. In some embodiments,layer portion 1906 can be a remote phosphore operating within the core,formed by layers 1901-1902, of a non-imaging waveguide for the purposeof down-conversion of the light incident on facet 1903.

FIG. 20A shows a rendering of an edge emitting diode 2020 with threelayers comprising the light emitting waveguide structure of a lightemitting diode or pin structure, n-portion 2003, p-portion 2001, andquantum well 2004 of the diode. The quantum well 2004 represents thecombination region which may emit, for example blue light. A taperedcore portion 2002 of a facet coupled waveguide device 2014 is shownhaving and an optical size equal to and aligned with the light emittingportion of the diode. In some embodiments, the tapered core 2002 has anindex which decreases from left to right and thickness that decreasesfrom left to right. Tapered core 2002 may be the core portion of thedevice shown FIG. 19 above (i.e. layers 1901 through 1902 and 1906.

FIG. 20B illustrates device 2014 with tapered core 2002 as illustratedin FIG. 20A within a waveguide structure coupled with diode 2020. Asillustrated, tapered core 2002 is surrounded by cladding 2010, substrate2011, and cladding 2012. Cladding 2010 and 2012 are lower index to forma waveguide with substrate 2011. As shown in FIG. 20B, diode 2020 ismounted on heat sink 2024. Device 2014 is mounted on positioning block2026 so as to align with diode 2020. Heat sink 2024 and positioningblock 2026 are mounted on submount heat sink 2022. Diode 2020 withdevice 2014, heat sink 2024, positioning block 2026, and submount heatsink 2022 form a device 2030. FIG. 20C illustrates light propagationfrom the diode through tapered core 2002 and coupling into substrate2011 by mode-sized conversion. The light is laterally coupled into thetapered layer 2002 and wave guided in the tapered layer until that layercan no longer support a mode volume. At that lateral portion of thewaveguide, the light undergoes a mode size conversion into themacroscopic waveguide and undergoes a transition to ray opticpropagation in the macroscopic waveguide comprised of the substrate 2011with cladding layers 2010 and 2012. The light undergoes emission 2013 atthe free space facet of the macroscopic waveguide with a half angleillustrative of the contrast between substrate 2011 and cladding layers2010 and 2012.

FIG. 21 shows device 2030, which includes the coupled waveguidestructure 2014 of FIG. 20C showing the packaging of diode 2020 with twoheat sink structures 2022, one on either primary planar side of thediode 2020.

FIG. 22 shows a device 2032 that includes three diodes 2020-1 through2020-3 that overlap waveguide structure 2014. Diodes 2020-1 through2020-3 can represent red, green, and/blue (RGB) drivers, respectively.

FIG. 23A shows device 2030, which is a luminaire coupler planar packagewith a diode source 2020 with two sided thermal heat sinks 2022, next toa Cree LMH6 luminaire 2306. Device 2030 can have an NA of 0.087 with alight output cone half angle of 5 degrees. According to at least someaspects of the present invention, the planar waveguide coupler basedluminaire may have an output luminance equivalent to the Cree LMH6 in amuch smaller package as shown.

FIG. 24 shows three edge emitting diode device 2032, right aligned witha waveguide coupler transformer 2014 according to the present invention.Emitted light cone 2401 is a mixture of light from the three diodes2020-1 through 2020-3.

FIG. 25 shows device 2032 packaged on the surface of a substrate 2501,which may be a thermal electric submount. The waveguide coupler includesa method of alignment and through holes for fastening. FIG. 26 showsdevice 2032 joined to a heat dissipation device 2601 and mounted on apackage 2602. FIG. 27 shows two devices 2032 as shown in FIG. 25fastened to a heat dissipation device.

FIG. 28 shows a device 2803 coupled to three diodes 2020. Device 2803 isa tapered coupler constructed similarly to device 2032 so as toconcentrate light emission 2801. Device 2803 has an in-plane physicaltaper, which concentrate the light from diodes 2020. The couplertransformer is a non-imaging concentrator with an optical area less thanor equal to the area of one or more diode light sources.

FIG. 29 shows a coupler transformer according to some embodiments of thepresent invention. The coupler transformer illustrated FIG. 29 includesin the core of the waveguide one or more layers 2902, 2903, and 2904between cladding layer 2901 and waveguide core 2910. The couplertransformer also includes a lower cladding 2911. One or more of layers2901, 2902, 2903, or 2904 are doped with a phosphor or are an activeoptical material or semiconductor. This device is a coupler between lowNA devices, as shown by half angles 2905 and 2906. A doped layer asdiscussed above can provide an active component to the coupler device.

FIG. 30A and FIG. 30B show the plan and perspective view, respectively,of a substrate with three offset layers. Offset layers 3001, 3002, and3003 can be made to have tapered lateral thickness profile according tosome embodiments of the present invention similar to the profile of thelayers 2901, 2902, 2903 or 2904 of FIG. 29. Layer 3002 can be anintrinsic semiconductor layer that insulates and separates doped PN oranode layers 3001 and 3003 to form a vertical PIN structure to conductlight laterally through the core of a waveguide. In some embodiments,layers 3001 and 3003 are conductive transparent layers. All layers areshown on a waveguide core 3000, having a lower index than depositedlayers 3001, 3002, and 3003.

FIGS. 31A and 31B show the three offset layers 3101, 3102, and 3103 on asubstrate 3100 similar to that shown in FIGS. 30A and 30B to form device3110. Layers 3101, 3102, and 3103 are tapered versions of layers 3001,3002, and 3003, respectively. Metallization 3105 is coupled to layer3103 and metallization 3104 is coupled to layer 3101. FIG. 31B shows thepath of light 3107 laterally through the PIN waveguide core from source3106. FIGS. 32A and 32B shows electrical connection to device 3110. Asis illustrated, multiple ones of device 3110 can be serially connectedin the path of a light beam. Wires 3202 and 3203 serially couplemultiple ones of devices 3110. Such a series of devices 3110 can be usedas laterally absorbing solar cells formed in the code of a waveguide andconnected in series so as to provide additive voltage at a reducedcurrent. The band absorber materials may be the same or different. Theband absorber materials in successive devices can be any suitablematerial, for example germanium, silicon CdTe, CIGS or a GaN or GaAs orIndium Phosphide based absorber.

FIG. 33 shows a lateral absorbing photovoltaic cell device 3110 in awaveguide receives source light 3106. A series transformer mode sizeconverter 3303 according to some embodiments of the present inventioncan be used for out coupling below band light from device 3110 into anoptical fiber 3306 with core 3307 for transport.

FIG. 34 shows a system for the concentration, coupling and transport oflight to an optical receiver 3406. As shown in FIG. 34, solar light canbe concentrated by mirror 3402 to form source light 3106 that is coupledinto device 3310 as described above. Light not absorbed by the PINjunction in device 3310 is coupled into optical fiber 3306 andtransported to optical coupler 3404. Optical coupler 3404 can be formedaccording to embodiments of the present invention and couples light fromfiber 3306 to optical receiver 3406. The light can be absorbed andstored as thermal energy in receiver 3406.

FIG. 35 illustrates optical attenuation in ZBLAN as compared withSilica. ZBLAN is part of the family of heavy-metal fluoride glasses.Ordinary glass is based on silica, molecules of silicon dioxide (likesand or quartz), plus other compounds to get different qualities (mosteyeglasses, though, are made of special plastics). ZBLAN is fluorinecombined with metals: zirconium, barium, lanthanum, aluminum, and sodium(Zr, Ba, La, Al, Na, hence the name).

One skilled in the art will recognize variations and modifications ofthe examples specifically discussed in this disclosure. These variationsand modifications are intended to be within the scope and spirit of thisdisclosure. As such, the scope is limited only by the following claims.

What is claimed is:
 1. A solar cell comprising: a waveguide core forreceiving light; a first layer formed on the waveguide core; a secondlayer formed on the first layer; a third layer formed on the secondlayer; first metalization coupled to the first layer; and secondmetalization coupled to the third layer; wherein the first layercomprises a first optical film which varies in an index of refraction ina lateral direction between a first input end where the light isreceived and a first output end where the light is emitted.
 2. The solarcell of claim 1, wherein the second layer is an intrinsic layer thatseparates the first and third layers.
 3. The solar cell of claim 1,wherein one or more of the first, second, or third layers has a taperedlateral thickness.
 4. The solar cell of claim 1, wherein one or more ofthe first layer or the third layer is a conductive transparent layer. 5.The solar cell of claim 1, wherein the first, second, and third layersform a PIN device.
 6. The solar cell of claim 5, wherein the PIN deviceincludes a band absorber material selected from a group consisting ofgermanium, silicon, CdTe, CIGS, GaN, GaAs, and indium phosphide.
 7. Thesolar cell of claim 1, wherein the waveguide core has a first index ofrefraction that is lower than respective indexes of refraction for thefirst, second, and third layers.
 8. A method comprising: receiving, by asolar cell, light, the solar cell comprising: a waveguide core forreceiving the light; a first layer formed on the waveguide core; asecond layer formed on the first layer; a third layer formed on thesecond layer; first metalization coupled to the first layer; and secondmetalization coupled to the third layer; wherein the first layercomprises a first optical film which varies in an index of refraction ina lateral direction between a first input end where the light isreceived and a first output end where the light is emitted; andgenerating a voltage.
 9. The method of claim 8, wherein the second layeris an intrinsic layer that separates the first and third layers.
 10. Themethod of claim 8, wherein one or more of the first, second, or thirdlayers has a tapered lateral thickness.
 11. The method of claim 8,wherein one or more of the first layer or the third layer is aconductive transparent layer.
 12. The method of claim 8, wherein thefirst, second, and third layers form a PIN device.
 13. The method ofclaim 12, wherein the PIN device includes a band absorber materialselected from a group consisting of germanium, silicon, CdTe, CIGS, GaN,GaAs, and indium phosphide.
 14. The method of claim 8, wherein thewaveguide core has a first index of refraction that is lower thanrespective indexes of refraction for the first, second, and thirdlayers.
 15. A solar cell comprising: a waveguide core for receivinglight; a first PIN device formed on the waveguide core; a second PINdevice formed on the waveguide core and coupled in series with the firstPIN device; wherein the first PIN device comprises: a first layer formedon the waveguide core; a second layer formed on the first layer; a thirdlayer formed on the second layer; first metalization coupled to thefirst layer; and second metalization coupled to the third layer; whereinthe first layer comprises a first optical film which varies in an indexof refraction in a lateral direction between a first input end where thelight is received and a first output end where the light is emitted. 16.The solar cell of claim 15, further comprising a conductor electricallycoupling the second metalization to a third metalization of the secondPIN device.
 17. The solar cell of claim 15, wherein the first PIN deviceand the second PIN device include a same band absorber material.
 18. Thesolar cell of claim 15, wherein the first PIN device and the second PINdevice include a different band absorber material.
 19. The solar cell ofclaim 15, wherein the first PIN device includes a band absorber materialselected from a group consisting of germanium, silicon, CdTe, CIGS, GaN,GaAs, and indium phosphide.
 20. The solar cell of claim 15, wherein oneor more of the first, second, or third layers has a tapered lateralthickness.